Liquid urethane filled subframe bushings

[BigKriss]

I filled them up using Flexane 80A. It takes up to a week for them to set at room temperature.
http://img241.imageshack.us/img241/7876/bush44ug.jpg
http://img241.imageshack.us/img241/9413/bush18oi.jpg
I first did the bottom side and there was a break in one of the bushings rubber meaning the urethane poured into the other half of the bushing when it was upside down.

not so good bushing with urethane slowly went down. I didn't bother putting new urethane over the 12 hour old set stuff.
http://img230.imageshack.us/img230/5208/bush32an.jpg

better bushing
http://img230.imageshack.us/img230/1905/bush22dt.jpg

[nuclearfusion]

We used this technique on four E28s in 1999. Devcon Flexane 80 with FL-20 primer, left cure for a few days before installing, etc.

All four cars belonged to local club members and all are driven pretty hard quite regularly. One E28 M5, two 535i's and one 533i. As far as I know all of them are still using these bushings 7 years later and none have worn out so far. That's saying a lot given these guys and how they drive their cars.

I didn't notice any very great increase in harshness or differential noise, etc. and believe overall the urethane fill was a good improvement. I'd recommend it.

Enjoy!

Fusion

[BigKriss]

Yeah I used the FL-20 Primer, I put that on after I first cleaned the surface with acetone and a cloth. They fl-20 stayed on for 1/2 an hour then I made up the mixture. I have Bruno's delrin rings to install also. It costs aud$35 for the primer and aud$80 for the Devcon Flexane 80 (1 pound - 450grams).

[nuclearfusion]

Yeah I used the FL-20 Primer, I put that on after I first cleaned the surface with acetone and a cloth. They fl-20 stayed on for 1/2 an hour then I made up the mixture. I have Bruno's delrin rings to install also. It costs aud$35 for the primer and aud$80 for the Devcon Flexane 80 (1 pound - 450grams).

OK, I dragged out my invoice from '99 on these parts. (!) The FL-20 was $CAD 17 and Flexane 80 was $CAD 47. Probably more expensive now.

My strategy was to cut out the mold pouring flash from the centre of the bushings, tape the bottom of them and pour them full of urethane all at once from the top. A bit of agitation with a stiff wire all around the edge surfaces to ensure good adhesion and remove bubbles seemed to help.

In all the time I had the bushings in my E28 (7 years) I never saw the urethane delaminate from the rubber substrate of the bushing shell. We were careful to prep the rubber surfaces really well, much as Kriss did, and apply the FL-20 primer well in advance. I think we painted it on and let it dry per instructions before pouring the flexane.

It's a messy job as I recall, and urethane cleanup is a total bear so I'd advise elbow-length nitrile surgeon's-style gloves for this one.

Enjoy!

Fusion

[BigKriss]

Nice comments there mate. I didn't use gloves though. The taping of the bushes sounds better to do all at once. Maybe that way is better but it shouldn't matter too much.

[BillionPa]

so, im gonna do this soon, wondering if there is any logic to go to a thinner or thicker version of the liquid urethane. its available in 60A and 94A hardness.... 94 is the thicker one.

[BigKriss]

No idea, I could only get 80A or 94A.


so, im gonna do this soon, wondering if there is any logic to go to a thinner or thicker version of the liquid urethane. its available in 60A and 94A hardness.... 94 is the thicker one.

[neil_004]

Let us know your opinion on how they feel when you get them in.

[jjdickm]

What is the benefit of using a liquid urathane on a subframe bushing? does it last longer or does it make the car more ridgid? also where do you pick up this stuff?

[Brandon J]

What is the benefit of using a liquid urathane on a subframe bushing? does it last longer or does it make the car more ridgid? also where do you pick up this stuff?

The benefit is to fill-in the holes/open space of the bushing with something durable. By fillin-in the open space, there will be less flex and less fatigue on the bushing. BMW dials in the flex to smooth out the ride and harshness from abrupt acceleration and braking. The liquid urethane is easy to work with so it is commonly used.

[BillionPa]

radford bros sells it, $44 for a pound of Flexane 80A + FL20 primer.

[Dash01]

Hasn't 3M Windo-Weld super fast urethane PN 0806089 (~$14 per caulking-gun 10.5 fl. oz. size applicator tube) been used for such applications? Available at car parts stores everywhere, it is commonly used to mount windshields, etc..

Supposedly, it cures to hardness about like skate board wheels, is extremely tough, and has been used by ricers and Porsche guys to upgrade their suspensions, for years.

Some guys just glob this stuff on their old, broken bushings, etc. using duct tape to keep it in place while curing overnight, without necessarily even removing said bushings from the car. Reportedly, the different hardnesses of the old rubber and the new Windo-Weld urethane act synergistically, as rubber has one vibration dampening coefficient, and urethane has another, with the binary combination better than either. That's what I've read, but am neither a chemical engineer nor play one on TV.

If this works, presumably you would not need to bother removing or replacing your subframe bushings, etc..

[BillionPa]

you would remove the 13+ year old bushings to put new ones in that dont suck, obviously :D

urethane on a bushing that isnt broken is better than on a bushing that is broken. also an old bushing would be dirty, and it would be really hard to get to the side of it thats inside the body of the car.

you want the bushing to be clean enough to eat off of, and primed for proper adhesion.

[Russell]

Going to try it. Bought the windo-weld at Advance auto parts today. Hope to try this weekend if the weather is not too cold.

My sub frame bushings are original at 134,000 miles. Bruno's inserts helped re vertical movement. However, I think there is some side-to-side movement causing rear steering.

[brick8]

Are you going to do it without removing the bushings as Dash10 suggests? Would be great if it works!

[Russell]

Yes, without removing bushings. Not sure yet on technique. Might be able to fill from top with a tube. If so, might be able to cover bottom of the bushing with duct tape/piece of wood and the put cover plate/bolt on until it sets up. about 15 minutes working time.

Or, since the material is similar in thickness to household caulk, I might be able to squirt it up into the cavities, quickly tape/wood and put cover plate on until it sets up.

Either way, I expect to use gloves, fingers, putty knife etc. to force it into the cavities. First I plan to clean a bit with 3m adhesive remover and acetone.

I just hope the process will reduce lateral movement of the subframe. Brunos inserts have reduced the vertical movement some..

[Russell]

heard that even if you fill in the voids, the materials will separate in about 6 months. Still going to try it this weekend. If it helps with rear steering and fails later, it will verify the problem.

[billy]

why go to all that bother when you can buy polyurethane bushes from powerflex for next to nothing?

[brick8]

I think he is going to try to do it without removing the bushings which we be a major hassle.

[Jon K]

Billy - powerflex makes urethane subframe bushings?

[DanH]

These must be the Powerflex bushings (http://www.powerflex.co.uk/products.asp?cat=0003&catalog=0903) that Billy was referring to. It looks like they make an E34 kit for both the front and rear. Looks like they are in the U.K.


Billy - powerflex makes urethane subframe bushings?

[DanH]

Here is a U.S. source of the powerflex bushings for $87/pair (select part 6 in the menu): http://www.nexternal.com/powerflex/Product33

These must be the Powerflex bushings (http://www.powerflex.co.uk/products.asp?cat=0003&catalog=0903) that Billy was referring to. It looks like they make an E34 kit for both the front and rear. Looks like they are in the U.K.

[BillionPa]

O_O

well hot damn, might as well get those and forget the week of prepping.

[Jon K]

Nice I'll be buying these in the spring

[BillionPa]

anyone else notice the wording for the from control arm bushings on the powerflex page are either reversed by accident or just wrong?

[BigKriss]

I tried removing the subframe bushes about 2 weeks ago but after I got the car jacked in the air. I have a lot of trouble removing the subframe pins. I mean I tried for around 30mins to remove one and I couldn't do it. Fustrated, I'm taking it to a shop soon and I'm going to get them to remove and install them.

The powerflex subframe bushes have been talked about quite a bit over on m5board.com like here - http://www.m5board.com/vbulletin/showthread.php?t=64785&highlight=subframe+powerflex

Maybe I have gone to a lot of trouble but new bushes with the liquid urethane and the delrin subframe plates, how much firmer would you want the bush to be?